I have recently found out that glassdoor use negative company reviews as leverage to squeeze some kind of membership subscription out of companies.
Myself and a host of other employees who walked out of a company (due to be asking to do some things that were basically illegal) had left 100% honest reviews on glassdoor about the company to warn off anybody who might be suckered into employment there. Roll on five weeks, they have all been deleted. We had been warned that this might happen so instead of writing seething reviews, we made sure that the reviews were very well balanced and refrained from mentioning the illegal activities that we were asked to partake in.
Apparently once a company gets a few negative reviews glassdoor contacts them and makes them aware of the reviews. Glassdoor suggests that the company sign up for a paid subscription which will result in each review being scrutinised under much stricter posting rules... rules which apparently only about 8% of reviews manage to get past.
So glassdoor is basically a scam.